Permanent magnet synchronization motor vector control device

ABSTRACT

A vector control device for a permanent magnet synchronous motor drive by an inverter. The vector control device includes: a current command generation unit for generating a d-axis current command id* and q-axis current command iq* from a given torque command T*; and a current control unit operating so that the motor current coincides with the current command. The current command generation unit includes: d-axis basic current command id 1 * by using the torque command; a limiter unit for inputting the current command id 1 * and outputting a value limited to below zero as a second d-axis basic current command id 2 *; a d-axis current command compensation unit for outputting the current command id 2 * corrected in accordance with the d-axis current command compensation value dV as a d-axis current command id*; and a q-axis current command generation unit for generating a q-axis current command iq* from the d-axis current command id*.

TECHNICAL FIELD

The present invention relates to a permanent magnet synchronous motorvector control device, and more particularly to a permanent magnetsynchronous motor vector control device provided with a current commandgeneration unit that can obtain by use of a simple mathematicalexpression a d-axis current command id* and a q-axis current command iq*capable of realizing maximum torque control.

BACKGROUND ART

The technology of vector-controlling a permanent magnet synchronousmotor by use of an inverter is widely utilized in the industrial fields;by separately operating the amplitude and the phase of the outputvoltage of the inverter, the current vector in the motor is optimallyoperated so that the torque of the motor is instantaneously controlledat high speed. Because, compared with an induction motor, magnetic fluxis ensured by means of a permanent magnet, no excitation current isrequired, and because no current flows in the rotor, no secondary copperloss is produced; therefore, a permanent magnet synchronous motor isknown as a high-efficiency motor, and the application of a permanentmagnet synchronous motor to an electric vehicle control device has beenstudied in recent years. It is known that, in a magnet-embeddedpermanent magnet synchronous motor (i.e., interior permanent magnetsynchronous machine, and abbreviated as IPMSM, hereinafter), which hasbeen attracting people's attention in recent years, among permanentmagnet synchronous motors, torque thereof is efficiently obtained byutilizing reluctance torque, produced through a difference between rotormagnetic resistance values, in addition to torque produced by magneticflux caused by a permanent magnet.

However, it is known that, in an IPMSM, there exist a great number ofcombinations of d-axis current and q-axis current for generating giventorque. Furthermore, it is known that the characteristics of an IPMSMsuch as the amplitude of a current that flows in the IPMSM, the powerfactor, the iron loss, and the copper loss largely change depending onthe respective amplitudes of the d-axis current and the q-axis current,i.e., selection of the current vector. Accordingly, in order to operatean IPMSM efficiently, it is required to select an appropriate currentvector in accordance with the application and operate it. That is tosay, in a permanent magnet synchronous motor vector control device, itis required to generate an appropriate current command forinstantaneously controlling the vector of an electric current that flowsin a motor so that the current vector satisfies desired conditionsdescribed below; therefore, it is important in terms of configuring asystem how to configure a current command generation unit that generatesa current command from a torque command.

Methods of selecting a current command include a method of making theefficiency of a motor maximum, a method of making the power factor ofthe motor to be “1”, a method of making torque obtained with giveninterlink magnetic flux to be maximum, a method of making torqueobtained with a certain electric motor current to be maximum, and thelike; however, in terms of application to an electric vehicle controldevice, the method of making torque obtained with a given current to bemaximum (referred to as “maximum torque control”, hereinafter) isoptimal because, by utilizing this method, the current rating of aninverter can be minimized while the high-efficiency operation of a motorcan be performed, whereby the loss in the inverter can also beminimized.

As a related conventional technology, Patent Document 1 discloses amethod in which the respective optimal values of a d-axis current id anda q-axis current iq corresponding to various kinds of torque values of amotor are preliminarily measured and mapped; during operation of themotor, the map is referred to, as may be necessary, in response to atorque command, and a d-axis current command id* and a q-axis currentcommand iq* corresponding to the torque command are obtained; then,current control is performed in such a way that the electric currentscorrespond to the d-axis current command id* and the q-axis currentcommand iq*.

[Patent Document 1] Japanese Patent Application Laid-Open Pub. No.2006-121855

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the method in which a map is referred to is not preferable,because, in order to create the map, there is required a working step inwhich electric currents are measured while a motor is operated withvarious kinds of torque values, and then optimal combinations of ad-axis current id and a q-axis current iq are decided, and thereby ittakes considerable time and labor to create the map, and becausemounting of the map in an actual vector control device cannot readily becarried out, for example, for the reason that the map becomes large incapacity and complicated, and a large memory capacity is required inorder to store the map.

The present invention has been implemented in order to solve theforegoing problems; the objective thereof is to provide a permanentmagnet synchronous motor vector control device including a currentcommand generation unit that can obtain a d-axis current command id* anda q-axis current command iq* with which maximum torque control can berealized by use of a simple calculation expression, without utilizingany map, and that can readily be mounted in an actual vector controldevice.

Means for Solving the Problems

A permanent magnet synchronous motor vector control device according tothe present invention separates an electric current in a permanentmagnet synchronous motor, driven by an inverter that converts a DCvoltage into an arbitrary-frequency AC voltage and outputs the ACvoltage, into a d-axis current id and a q-axis current iq that arequantities on a d axis and a q axis, respectively, and rotate insynchronization with a rotation electric angle of the permanent magnetsynchronous motor, and controls the d-axis current id and the q-axiscurrent iq. The vector control device includes a current commandgeneration unit that generates a d-axis current command id* and a q-axiscurrent command iq* from a given torque command; and a current controlunit that operates in such a way that the currents in the motor coincidewith the respective current commands. The current command generationunit is provided with a d-axis basic current command generation unitthat utilizes the torque command so as to generate a first d-axis basiccurrent command id1*; a limiter unit that receives the first d-axisbasic current command id1* and outputs a value limited to below zero, asa second d-axis basic current command id2*; a d-axis current commandcompensation unit that receives the second d-axis basic current commandid2* and outputs as the d-axis current command id* a value obtained bycorrecting the second d-axis basic current command id2* in accordancewith a d-axis current command compensation value dV outputted from thecurrent control unit; and a q-axis current command generation unit thatgenerates a q-axis current command iq* from the d-axis current commandid*, and the current command generation unit generates the d-axiscurrent command id* and the q-axis current command iq* capable ofgenerating with minimum currents the torque corresponding to the torquecommand.

Advantages of the Invention

A permanent magnet synchronous motor vector control device according tothe present invention makes it possible to realize the maximum torquecontrol by use of a simple calculation expression, without utilizing anymap, and to obtain in a high-speed region the d-axis current command id*and the q-axis current command iq* that enable the control in a weakenedmagnetic flux; therefore, there can be obtained a permanent magnetsynchronous motor vector control device having a current commandgeneration unit that can readily be mounted in an actual vector controldevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the configuration of apermanent magnet synchronous motor vector control device according toEmbodiment 1 of the present invention;

FIG. 2 is a graph representing the relationship between the torque curveand the curve indicating the minimum current condition, according toEmbodiment 1 of the present invention;

FIG. 3 is a block diagram illustrating the configuration of a currentcommand generation unit according to Embodiment 1 of the presentinvention; and

FIG. 4 is a block diagram illustrating the configuration of a currentcommand generation unit according to Embodiment 2 of the presentinvention.

DESCRIPTION OF REFERENCE NUMERALS

-   1: CAPACITOR-   2: INVERTER-   3, 4, 5: CURRENT DETECTOR-   6: MOTOR-   7: RESOLVER-   8: VOLTAGE DETECTOR-   10: CURRENT COMMAND GENERATION UNIT-   11: D-AXIS BASIC CURRENT COMMAND GENERATION UNIT-   12: LIMITER UNIT-   13: ABSOLUTE-VALUE CIRCUIT-   14: ADDER (D-AXIS CURRENT COMMAND COMPENSATION UNIT)-   15, 15A: Q-AXIS CURRENT COMMAND GENERATION UNIT-   20: CURRENT CONTROL UNIT-   100: VECTOR CONTROL DEVICE

Best Mode for Carrying Out the Invention

Embodiment 1

FIG. 1 is a diagram illustrating the configuration of a permanent magnetsynchronous motor vector control device according to Embodiment 1 of thepresent invention. As illustrated in FIG. 1, the main circuit of thepermanent magnet synchronous motor vector control device according toEmbodiment 1 is configured with a capacitor 1 that serves as a DC powersource, an inverter 2 that converts a DC voltage across the capacitor 1into an AC voltage of an arbitrary frequency, and a permanent magnetsynchronous motor (referred to simply as a motor, hereinafter) 6. In acircuit, there are arranged a voltage detector 8 that detects thevoltage across the capacitor 1 and current detectors 3, 4, and 5 thatdetect currents iw, iv, and iu, respectively, in the output lines of theinverter 2; in the motor 6, there is disposed a resolver 7 that detectsrotor position information θm; the respective detection signals areinputted to a vector control device 100.

In addition, the resolver 7 may be replaced by an encoder, or a positionsignal obtained through the resolver 7 may be replaced by a positionsignal obtained in accordance with a sensor-less method in which theposition signal is calculated based on a voltage and a current; in suchcases, the resolver 7 is not required. In other words, the method forobtaining a position signal is not limited to the method in which theresolver 7 is utilized. Additionally, as far as the current detectors 3,4, and 5 are concerned, when the current detectors are provided for atleast two phases, the current for the remaining phase can be obtainedthrough a calculation; thus the permanent magnet synchronous motorvector control device may be configured in such a way as describedabove. The output currents of the inverter 2 may be obtained throughreproduction from the DC-side currents of the inverter 2.

Gate signals U, V, W, X, Y, and Z generated by the vector control device100 are inputted to the inverter 2 so that switching elementsincorporated in the inverter 2 are PWM-controlled. As the inverter 2, avoltage source PWM inverter is preferably utilized; because theconfiguration thereof is publicly known, detailed explanation thereforwill be omitted. A torque command T* is inputted from an unillustratedhigher-hierarchy control device to the vector control device 100; thevector control device 100 controls the inverter 2 in such away that thetorque generated by the motor 6 coincides with the torque command T*.

Next, the configuration of the vector control device 100 will beexplained. The vector control device 100 is configured with a currentcommand generation unit 10 and a current control unit 20.

The current command generation unit 10, which is a main part of thepresent invention, has a function of receiving the torque command T* anda d-axis current command compensation amount dV and generating a d-axiscurrent command id* and a q-axis current command iq*. The d-axis currentcommand compensation amount dV is an amount for correcting the d-axiscurrent command id* so as to operate the motor 6 in a weakened magneticflux so that, in a high-speed region, the induced voltage of the motor 6does not exceed the outputtable maximum voltage of the inverter 2. As anexample of calculation method for the d-axis current commandcompensation amount dV, there exists, for example, a publicly knowntechnology in which, in the case where the voltage command to the motor6 exceeds a given setting value, the d-axis current command compensationamount dV (becomes below zero) is generated in accordance with theexcess amount; however, because the specific configuration thereof is noobject herein, explanation therefor will be omitted. In addition,because the current command generation unit 10 is the main part of thepresent invention, explanation therefor will be made later.

The current control unit 20 receives the DC voltage EFC for the inverter2 and the positional information θm for the motor 6 and converts theelectric motor currents iu, iv, and iw on the three-phase static axesdetected at the output-side of the inverter 2 into a d-axis current idand q-axis current iq, which are electric currents converted intoamounts on the dq coordinates that rotate in synchronization with therotation electric angle of the motor. Additionally, the current controlunit 20 has a function of deciding on/off-switching of the gate signalsU, V, W, X, Y, and Z inputted to the inverter 2 in such a way that thed-axis current id and the q-axis current iq coincide with the d-axiscurrent command id* and the q-axis current command iq*, respectively,generated by the current command generation unit 10. In addition, agreat number of publicly known technologies can be applied to theconfiguration of the current control unit 20; therefore, explanationtherefor will be omitted.

A basic principle, which is required to understand the configuration ofthe current command generation unit 10 that is the main part of thepresent invention, will be explained below.

The condition (referred to as a minimum current condition, hereinafter)for the d-axis current id and the q-axis current iq for realizingmaximum torque control in which maximum torque is obtained with a givenelectric current is given by the equation (1) below, which is alreadypublicly known.

$\begin{matrix}{i_{d} = {\frac{\phi_{a}}{2\left( {L_{q} - L_{d}} \right)} - \sqrt{\frac{\phi_{a}^{2}}{4\left( {L_{q} - L_{d}} \right)^{2}} + i_{q}^{2}}}} & (1)\end{matrix}$where L_(d) denotes a d-axis inductance (H); L_(q), a q-axis inductance(H); φ_(a), permanent magnetic flux (Wb); i_(d), a d-axis current (A);and i_(q), a q-axis current (A).

In the case where given torque T is generated, by deciding the d-axiscurrent id and the q-axis current iq in such a way as to satisfy theequation (1), the magnitude of the current vector formed of id and iqcan be minimized. In other words, the amplitude of the current in themotor 6 can be minimized.

Meanwhile, the torque T generated by the motor 6 is given by theequation (2) below.T=P _(n){φ_(a) i _(q)+(L _(d) −L _(d))i _(d) i _(q)}  (2)where Pn denotes the number of pole pairs in the motor 6.

By rearranging the equation for the q-axis current iq, the equation (3)below is yielded.

$\begin{matrix}{i_{q} = \frac{T}{P_{n}\left\{ {\phi_{a} + {\left( {L_{d} - L_{q}} \right)i_{d}}} \right\}}} & (3)\end{matrix}$

By solving the simultaneous equations consisting of the equation (1) andthe equation (3) so as to obtain id and iq, there can be obtained thecombination, of the d-axis current id and the q-axis current iq, thatcan generate given torque T with minimum currents.

Here, it is theoretically possible that, by, in the equations (1) and(3), reading the torque T as the torque command T*, the d-axis currentid as the d-axis current command id*, and the q-axis current iq as theq-axis current command iq* and solving the simultaneous equationsconsisting of the equation (1) and the equation (3) for id* and iq*,there are obtained the d-axis current command id* and the q-axis currentcommand iq* capable of generating with a minimum electric current thetorque T that coincides with the torque command T*.

FIG. 2 is a graph representing the relationship between the torque curveand the curve indicating the minimum current condition, according toEmbodiment 1 of the present invention. The relationship between thetorque curve and the curve indicating the minimum current conditionrepresents the relationships in the equations (1) and (3) with thed-axis current id as the abscissa and the q-axis current iq as theordinate. Each of the curves from the top right to the bottom left is atorque curve rendered by substituting power-running torque T (=50 Nm to1500 Nm) for the torque T in the equation (3). The curve Imi from thetop left to the bottom right is a curve indicating the minimum currentcondition represented by the equation (1); the curve Imi represents thecombination of the d-axis current id and the q-axis current iq capableof generating given torque T with minimum currents.

The d-axis current id and the q-axis current iq capable of generatinggiven torque T with minimum currents can be obtained by calculating theintersection point of the curve Imi indicating the equation (1) with thecurve Tor indicating the equation (3) in FIG. 2. In FIG. 2, for Pn, Ld,Lq, and φa in the equations (1) and (3), there are set constants thatare decided by imagining an electric vehicle driving motor whose outputpower is approximately 300 KW.

In addition, the torque curve and a curve indicating the minimum currentcondition in the case of a regenerative period are located in theunrepresented third quadrant in FIG. 2 and correspond to the respectivecurves rendered symmetrically with the curves in the case of a powerrunning period, represented in FIG. 2, with respect to the abscissa.Accordingly, for that reason, the curves in the case of a regenerativeperiod can also be presumed from the curves in the case of a powerrunning period represented in FIG. 2. Specifically, as can be seen fromFIG. 2, in the case where the power-running torque of 1300 Nm as thetorque T is generated, the minimum current condition is the combinationof id of approximately −200 A and iq of approximately 237 A; thus, inthe case where the regenerative torque of −1300 Nm as the torque T isgenerated, the minimum current condition is the combination of id ofapproximately −200 A and iq of approximately −237 A. It goes withoutsaying that the torque curve and a curve indicating the minimum currentcondition in the case of a regenerative period may be provided inaddition to the curves in the case of a power running period so that thed-axis current id and the q-axis current iq that satisfy the minimumcurrent condition are obtained.

Meanwhile, in order to calculate the intersection point of the curve Imirepresented by the equation (1) with the curve Tor represented by theequation (3), it is required to solve the simultaneous equations,consisting of the equation (1) and the equation (3), for id and iq;however, because the simultaneous equations result in a biquadraticequation, it is difficult to obtain solutions, whereby mounting in anactual vector control device is difficult. Accordingly, in manyconventional technologies, as described above, the d-axis current id andthe q-axis current iq that can generate given torque T with minimumcurrents are obtained by use of a map.

In contrast, the present invention is to calculate the d-axis current idand the q-axis current iq that can generate the torque T with minimumcurrents, in accordance with a simple calculation expression and withoututilizing any map. The foregoing method will be described in detailbelow.

It can be seen that, although being a quadratic curve, the curve Imi, inFIG. 2, indicating the minimum current condition is almost a straightline except for a region (id>−50 A, iq<75 A) where the d-axis current idand the q-axis current iq are small. Accordingly, in FIG. 2, there isrepresented by a broken line an approximate straight line Iap obtainedby applying a linear approximation to the curve indicating the minimumcurrent condition over a range except for a region (id>−50 A, iq<75 A)where the d-axis current id and the q-axis current iq are small. It canbe seen from FIG. 2 that the approximate straight line Iap is locatedapproximately on the curve indicating the minimum current condition.

In the application of controlling an electric vehicle, which is thesubject of the present invention, the case where the motor 6 is operatedin a region in which the d-axis current id and the q-axis current iq aresmall is limited, for example, to a constant-speed operation in whichthe motor 6 is operated with minute torque in order to maintain thespeed of the electric vehicle; therefore, the frequency of the foregoingcase out of the whole operation time is very low. Therefore, even in thecase where a linear approximation is applied to the curve indicating theminimum current condition, in most cases, the motor is operated underthe minimum current condition; thus, there exists no practical problem.

Let the approximate straight line for the curve, in FIG. 2, indicatingthe minimum current condition be given by the equation (4) below.i _(q) =ai _(d) +b  (4)

In the example in FIG. 2, the gradient a of the straight line is−1.0309, and the intercept b is 30.0. In the case where the approximatestraight line for the equation (4) is utilized, the d-axis current idand the q-axis current iq capable of generating given torque T withminimum currents can be obtained by calculating the intersection pointof the curve lap indicating the minimum current condition with the curveTor; the d-axis current id and the q-axis current iq can be obtained bysolving the simultaneous equations consisting of the equation (3) andthe equation (4). The simultaneous equations result in a quadraticequation that can readily be solved. By organizing the equations (3) and(4), the equations (5) below can be obtained.{aP _(n)(L _(d) −L _(q))}i _(d) ²+{(aP _(n)φ_(a))+bP _(n)(L _(d) −L_(q))}i _(d) +bP _(n)φ_(a) −T=0  (5)

Based on the equation (5), the d-axis current id is given by theequation (6) below.

$\begin{matrix}{i_{d} = \frac{\begin{matrix}{{- \left\{ {\left( {{aP}_{n}\phi_{a}} \right) + {{bP}_{n}\left( {L_{d} - L_{q}} \right)}} \right\}} -} \\\sqrt{\begin{matrix}{\left\{ {\left( {{aP}_{n}\phi_{a}} \right) + {{bP}_{n}\left( {L_{d} - L_{q}} \right)}} \right\}^{2} -} \\{4\left\{ {{aP}_{n}\left( {L_{d} - L_{q}} \right)} \right\}\left( {{{bP}_{n}\phi_{a}} - T} \right)}\end{matrix}}\end{matrix}}{2\left\{ {{aP}_{n}\left( {L_{d} - L_{q}} \right)} \right\}}} & (6)\end{matrix}$

From the equation (6), the d-axis current id capable of generating giventorque T with a minimum current, i.e., the d-axis current id thatrealizes the maximum torque control can be obtained. By substituting idgiven by the equation (6) for id in the equation (3), the q-axis currentiq is obtained.

In addition, a and b in the equation (6) may preliminarily be obtained,as represented in FIG. 2, from the approximate straight line for thecurve indicating the minimum current condition represented in theequation (1).

What has been described heretofore is the explanation for the principleof a method of obtaining the current vector capable of realizing themaximum torque control, i.e., the combination of the d-axis current idand the q-axis current iq.

Next, the configuration of a specific current command generation unit10, which is preferable for the vector control of a permanent magnetsynchronous motor, will be explained.

FIG. 3 is a diagram illustrating the configuration of a current commandgeneration unit 10 according to Embodiment 1 of the present invention.As illustrated in FIG. 3, from a torque command absolute value Tabs*obtained by passing the torque command T* through an absolute-valuecircuit 13 and the gradient a and the intercept b of the approximatestraight line indicating the minimum current condition represented bythe equation (4), a d-axis basic current command generation unit 11calculates a first d-axis basic current command id1*, based on theequation (7) below. The equation (7) is obtained by replacing the d-axiscurrent id and the torque T in the equation (6) by the first d-axisbasic current command id1* and the torque command absolute value Tabs*,respectively.

$\begin{matrix}{i_{d\; 1}^{*} = \frac{\begin{matrix}{{- \left\{ {\left( {{aP}_{n}\phi_{a}} \right) + {{bP}_{n}\left( {L_{d} - L_{q}} \right)}} \right\}} -} \\\sqrt{\begin{matrix}{\left\{ {\left( {{aP}_{n}\phi_{a}} \right) + {{bP}_{n}\left( {L_{d} - L_{q}} \right)}} \right\}^{2} -} \\{4\left\{ {{aP}_{n}\left( {L_{d} - L_{q}} \right)} \right\}\left( {{{bP}_{n}\phi_{a}} - {Tabs}^{*}} \right)}\end{matrix}}\end{matrix}}{2\left\{ {{aP}_{n}\left( {L_{d} - L_{q}} \right)} \right\}}} & (7)\end{matrix}$

The first d-axis basic current command id1* calculated in accordancewith the equation (7) is inputted to a limiter unit 12; in the casewhere id1* is positive, a second d-axis basic current command id2*,which is the output of the limiter unit 12, becomes “0”; in the casewhere id1* is negative, id2*, which is the output of the limiter unit12, becomes equal to id1*. In other words, the limiter unit 12 has afunction of limiting id2* not to become larger than zero.

As described above, by setting the upper limit value of the secondd-axis basic current command id2* to zero, it can be prevented that,particularly in a region where the torque command T* is small(approximately 50 Nm or smaller), the intersection point of the torquecurve with the approximate straight line indicating the minimum currentcondition occurs in the first quadrant (unrepresented), whereby thereare calculated the d-axis current command id* and the q-axis currentcommand iq* that are far away from the minimum current condition.

From another point of view, in a region where the torque command T* issmall, automatic transit to the control in which id is fixed to zero,which is a publicly known technology, can be performed. In addition, byutilizing in the equation (7) the torque command absolute value Tabs*,it is made possible to obtain the first d-axis basic current commandid1* by use of a single equation (7) both in the case where thepower-running torque is outputted and in the case where the regenerativetorque is outputted; therefore, the calculation can be simplified.

Next, the d-axis current command id* is obtained by adding the secondd-axis current command id2* and the d-axis current command compensationamount dV in an adder 14 that serves as a d-axis current commandcompensation unit. The d-axis current command compensation amount dV isa value below zero, which varies depending on the operation condition ofthe motor 6.

As described above, in the case where the rotation speed of the motor ismedium or low and the voltage for the motor 6 is the same as or lowerthan the maximum outputtable voltage of the inverter 2, the d-axiscurrent command compensation amount dV becomes zero, whereby the d-axiscurrent command id* that satisfies the minimum current condition can beobtained; in the case where, in a high-speed rotation region, thevoltage for the motor 6 exceeds the maximum outputtable voltage of theinverter 2, it is made possible to decrease the d-axis current commandid* in accordance with the d-axis current command compensation amountdV, whereby the motor 6 can be operated in a weakened magnetic flux.

Lastly, in a q-axis current command generation unit 15, by substitutingthe d-axis current command id* and the torque command T* for theequation (8) below, the q-axis current command iq* is obtained. Theequation (8) is obtained by replacing the d-axis current id, the q-axiscurrent iq, and the torque T in the equation (3) by the d-axis currentcommand id*, the q-axis current command iq*, and the torque command T*,respectively.

$\begin{matrix}{i_{q}^{*} = \frac{T^{*}}{P_{n}\left\{ {\phi_{a} + {\left( {L_{d} - L_{q}} \right)i_{d}^{*}}} \right\}}} & (8)\end{matrix}$

As described above, the permanent magnet synchronous motor vectorcontrol device according to Embodiment 1 of the present invention makesit possible to realize the maximum torque control by use of a simplecalculation expression, without utilizing any map, and to obtain in ahigh-speed region the d-axis current command id* and the q-axis currentcommand iq* that enable the control in a weakened magnetic flux. Thecontrol is performed by the current control unit 20 in such a way thatthe respective currents in the motor 6 coincide with the d-axis currentcommand id* and the q-axis current command iq* so that there can beobtained a permanent magnet synchronous motor vector control devicecapable of performing the maximum torque control of the motor 6.

The foregoing motor constants Ld, Lq, and φa, and the gradient a and theintercept b of the approximate straight line, which are utilized in therespective calculation expressions in the current command generationunit 10 may be changed at an arbitrary timing. For example, it isconceivable that the foregoing motor constants Ld, Lq, and φa, thegradient a, and the intercept b are changed in accordance with the speedof the motor 6, the magnitude of the torque, the amplitude of thecurrent, and the driving condition such as a power running period or aregenerative period, or that the foregoing motor constants Ld, Lq, andφa, the gradient a, and the intercept b are changed and adjusted inaccordance with the torque command T*, the d-axis current command id*,the q-axis current command iq*, or the d-axis current id and the q-axiscurrent iq which are detection values. In such a manner as describedabove, even in the region (id>−50 A, iq<75 A), in FIG. 2, where thed-axis current id and the q-axis current iq are small, a more accurateminimum current condition can be calculated; therefore, a more idealoperating point can be obtained.

In terms of ensuring the stability of the control system, it isdesirable that, in the case where the motor constants Ld, Lq, and φa,and the gradient a and the intercept b of the approximate straight lineare changed and adjusted, the speed of the motor 6, the magnitude of thetorque, the amplitude of the current, the torque command T*, and thed-axis current command id* and the q-axis current command iq*, or thed-axis current id and the q-axis current iq are referred to not directlybut after being processed through a delay element such as a lowpassfilter or a first-order delay circuit. In particular, the values of themotor constants Ld and Lq may change due to the effect of magneticsaturation; therefore, it is desirable to correct the values, as may benecessary.

Embodiment 2

FIG. 4 is a diagram illustrating the configuration of a current commandgeneration unit 10 in a permanent magnet synchronous motor vectorcontrol device according to Embodiment 2 of the present invention. Here,only constituent elements that differ from those of Embodiment 1illustrated in FIG. 3 will be explained, and explanations for similarconstituent elements will be omitted. As illustrated in FIG. 4, in acurrent command generation unit 10 according to Embodiment 2, the q-axiscurrent command generation unit 15 is replaced by a q-axis currentcommand generation unit 15A.

In the q-axis current command generation unit 15A, by substituting thed-axis current command id*, and the gradient a and the intercept b ofthe approximate straight line for the equation (9) below, the q-axiscurrent command iq* is obtained. The equation (9) is obtained byreplacing the d-axis current id and the q-axis current iq in theequation (4) by the d-axis current command id* and the q-axis currentcommand iq*, respectively.i _(q) *=ai _(d) *+b  (9)

In Embodiment 2, because the q-axis current command iq* is calculated inaccordance with the equation (9), the configuration of the expression issimpler than that of Embodiment 1 in which iq* is calculated inaccordance with the equation (8); therefore, the amount of calculationcan be suppressed, whereby an inexpensive microprocessor can beutilized.

The configurations described in the foregoing embodiments are examplesof the aspects of the present invention and can be combined with otherpublicly known technologies; it goes without saying that variousfeatures of the present invention can be configured, by modifying, forexample, partially omitting the foregoing embodiments, without departingfrom the scope and spirit of the present invention.

Moreover, in the foregoing embodiments, although the explanation for thepresent invention has been implemented in consideration of itsapplication to an electric vehicle, the application field of the presentinvention is not limited thereto; it goes without saying that thepresent invention can be applied to various related fields such as thefields of electric automobiles, elevators, and electric power systems.

The invention claimed is:
 1. A permanent magnet synchronization motorvector control device, applied to an electric vehicle control device,separating an electric current in a permanent magnet synchronizationmotor, driven by an inverter that converts a DC voltage into anarbitrary-frequency AC voltage and outputs the AC voltage, into a d-axiscurrent id and a q-axis current iq that are quantities on a d axis and aq axis, respectively, and rotate in synchronization with a rotationelectric angle of the permanent magnet synchronization motor, andcontrolling the d-axis current id and the q-axis current iq, the vectorcontrol device comprising: a current command generation unit thatgenerates a d-axis current command id* and a q-axis current command iq*from a given torque command; and a current control unit that operates insuch a way that the currents in the motor coincide with the respectivecurrent commands, wherein the current command generation unit isprovided with a d-axis basic current command generation unit thatutilizes the torque command so as to generate a first d-axis basiccurrent command id1*; a limiter unit that receives the first d-axisbasic current command id1* and outputs a value obtained by limiting thefirst d-axis basic current command id1* to below zero, as a secondd-axis basic current command id2*; a d-axis current command compensationunit that receives the second d-axis basic current command id2* andoutputs as the d-axis current command id* a value obtained by correctingthe second d-axis basic current command id2* in accordance with a d-axiscurrent command compensation value dV outputted from the current controlunit; and a q-axis current command generation unit that generates aq-axis current command iq* from the d-axis current command id*, and thecurrent command generation unit generates the d-axis current command id*and the q-axis current command iq* capable of generating with minimumcurrents the torque corresponding to the torque command, wherein thed-axis basic current command generation unit generates the first d-axisbasic current command id1*, by obtaining an intersection point of anequation (3) below indicating the relationship among the torque T, thed-axis current id, and the q-axis current iq of the motor with a linearequation (4) below that is obtained by applying a linear approximationto a curve indicating a condition under which the motor can generate agiven torque with minimum currents, over a range of the curve beingsubstantially straight line and excluding a region where a magnitude ofthe d-axis current id and a magnitude of the q-axis current iq aresmall, and that has a gradient and an intercept that represent therelationship between the d-axis current and the q-axis current, andwherein the first d-axis basic current command id1* is generated from afirst equation (7) below: $\begin{matrix}{i_{q} = \frac{T}{P_{n}\left\{ {\varphi_{a} = {\left( {L_{d} - L_{q}} \right)i_{d}}} \right\}}} & (3) \\{i_{q} = {{ai}_{d} + b}} & (4) \\{i_{d\; 1}^{*} = \frac{\begin{matrix}{{- \left\{ {\left( {{aP}_{n}\varphi_{a}} \right) + {{bP}_{n}\left( {L_{d} - L_{q}} \right)}} \right\}} -} \\\sqrt{\begin{matrix}{\left\{ {\left( {{aP}_{n}\varphi_{a}} \right) + {{bP}_{n}\left( {L_{d} - L_{q}} \right)}} \right\}^{2} -} \\{4\left\{ {{aP}_{n}\left( {L_{d} - L_{q}} \right)} \right\}\left( {{{bP}_{n}\varphi_{a}} - {Tabs}^{*}} \right)}\end{matrix}}\end{matrix}}{2\left\{ {{aP}_{n}\left( {L_{d} - L_{q}} \right)} \right\}}} & (7)\end{matrix}$ where Tabs* denotes the absolute value of the torquecommand; L_(d); a d-axis inductance (H); L_(q), a q-axis inductance (H);φ_(a), permanent magnetic flux (Wb); Pn, the number of pole pairs of themotor; a, the gradient of the linear equation; and b, the intercept ofthe linear equation.
 2. The permanent magnet synchronization motorvector control device according to claim 1, wherein any one of Ld, Lq,φa, a, and b in the first equation is changed at an arbitrary timing. 3.The permanent magnet synchronization motor vector control deviceaccording to claim 1, wherein any one of Ld, Lq, φa, a, and b in thefirst equation is changed in accordance with a signal including thed-axis current id and the q-axis current iq in the motor, the d-axiscurrent command id*, the q-axis current command iq*, and the torquecommand T*.
 4. The permanent magnet synchronization motor vector controldevice according to claim 1, wherein the q-axis current command iq* isgenerated by substituting the d-axis current command id* for a secondequation below:$i_{q}^{*} = \frac{T^{*}}{P_{n}\left\{ {\phi_{a} + {\left( {L_{d} - L_{q}} \right)i_{d}^{*}}} \right.}$where T* denotes the torque command; L_(d), a d-axis inductance (H);L_(q), a q-axis inductance (H); φa, permanent magnetic flux (Wb); andPn, the number of pole pairs of the motor.
 5. The permanent magnetsynchronization motor vector control device according to claim 4,wherein any one of Ld, Lq, and φa in the second equation is changed atan arbitrary timing.
 6. The permanent magnet synchronization motorvector control device according to claim 4, wherein any one of Ld, Lq,and φa in the second equation is changed in accordance with a signalincluding the d-axis current id and the q-axis current iq in the motor,the d-axis current command id*, the q-axis current command iq*, and thetorque command T*.
 7. The permanent magnet synchronization motor vectorcontrol device according to claim 1, wherein the q-axis current commandiq* is generated by substituting the d-axis current command id* for athird equation below:i _(q) *=ai _(d) *+b where a and b denote the gradient and theintercept, respectively, of the first equation.
 8. The permanent magnetsynchronization motor vector control device according to claim 7,wherein any one of a and b in the third equation is changed at anarbitrary timing.
 9. The permanent magnet synchronization motor vectorcontrol device according to claim 7, wherein any one of a and b in thethird equation is changed in accordance with a signal including thed-axis current id and the q-axis current iq in the motor, the d-axiscurrent command id*, the q-axis current command iq*, and the torquecommand T*.